This invention relates to methods for reacting aliphatic alcohol (alkanol), such as methanol or the like and olefinic hydrocarbons to produce lower alkyl tertiary-alkyl ethers.
In particular, this invention relates to a continuous integrated system for converting methanol to high octane ether by etherifying hydrocarbons containing iso-olefins, such as the C.sub.3 -C.sub.5 olefinic cracked gas streams obtained from fluid catalytic cracking (FCC) products.
It is known that isobutylene and other isoalkenes produced by hydrocarbon cracking may be reacted with methanol and other C.sub.1 -C.sub.4 lower aliphatic alcohols over an acidic catalyst to provide methyl tertiary butyl ether (MTBE) or the like. Generally, it is known that asymmetrical ethers having the formula (CH.sub.3).sub.3 C-O-R, where R is a C.sub.1 -C.sub.4 alkyl radical, are particularly useful as octane improvers for liquid fuels, especially gasoline.
MTBE, ethyl t-butyl ether (ETBE), tert-amyl methyl ether (TAME) and isopropyl t-butyl ether (IPTBE) are known to be high octane ethers. The article by J. D. Chase, et al., Oil and Gas Journal, Apr. 9, 1979, discusses the advantages one can achieve by using such materials to enhance gasoline octane. The octane blending number of MTBE when 10% is added to a base fuel (R+O=91) is about 120. For a fuel with a low motor rating (M+O=83) octane, the blending value of MTBE at the 10% level is about 103. On the other hand, for an (R+O) of 95 octane fuel, the blending value of 10% MTBE is about 114.
While it is known that isobutylene and/or isoamylene may be reacted with methanol over an acidic catalyst to provide MTBE and/or TAME, a problem of major importance in these processes is the separation of unreacted methanol and hydrocarbons from the etherification reaction product due to the proclivity of methanol to form a very dilute azeotropic mixture with hydrocarbons and the strong solubility of methanol in both water and hydrocarbons. But, to achieve high iso-olefin conversion to ethers equimolar or larger quantities of methanol are preferred in the etherification reaction.
In recent years, a major development within the petroleum industry has been the discovery of the special catalytic capabilities of a family of zeolite catalysts based upon medium pore size shape selective metallosilicates. Discoveries have been made leading to a series of analogous processes drawn from the catalytic capability of zeolites. Depending upon various conditions of space velocity, temperature and pressure lower oxygenates, such as methanol can be converted in the presence of zeolite type catalysts to olefins which can oligomerize to provide gasoline or distillate or can be converted further to produce aromatics. Recognizing the commonality of the feedstock and product between etherification reactions to produce high octane gasoline and zeolite catalyzed conversion reactions, interest has focused on the applicability of combined processes as an approach to advance the art in the production of high octane gasoline. While methanol or other reactive alkanols are converted by zeolite catalysis, minor amounts of other oxygenates are produced in the conversion process. Ketones, aldehydes and alkanoic acids found in the hydrocarbon effluent may be deleterious to its use as fuel.
It has been discovered that under certain conditions substantial improvements in the art of alkyl tert-alkyl ether production can be realized in a combination or integration of etherification and hydrocarbon conversion processes based upon zeolite type catalysis. Accordingly, it is an object of this invention to provide a novel integrated process for the production of alkyl tert-alkyl ethers, particularly MTBE and/or TAME.